1. Field of the Invention
The present invention relates to a system and method for monitoring the respiratory and heart rate of infants and adults, as well as other mammals, and in particular to a monitoring system that may be applied to areas of the body previously thought to be unsuitable for such monitoring.
2. Description of Related Art
Heart rate monitors employing photo rather than electrode means to acquire heart rate offer the advantage of a noninvasive electrodeless method of monitoring subjects. While there are accepted and practiced means that employ photo sensors to measure heart rate, current sensor designs have only been usable in highly perfused areas of the body that have underlying arterial blood supplies very close to the skin surface. Heart rate monitoring sites have been restricted to appendages, for example, finger tips, wrist (ulner and radial arteries), ear lobes, toes and ankles. These locations also exhibit large motion artifacts when moving that can cause discontinuous monitoring of heart rate during the movement. Traditionally, most commercial heart rate photo sensors are connected by means of a wire from the subject's sensor to the monitor.
For monitoring respiration, prior art inductive or capacitance plethmography respiration sensors typically embody coils of wire or conductive material that wrap almost completely around the subject's thoracic area. Typically inductive sensors sense motion by stretching the coil, thereby causing the mutual inductance of the entire coil to respond to any motion or stretching of the coil. These types of sensors produce very reliable and artifact resistant respiration signal analogs when compared to the conventional trans-thoracic impedance (TIP) methods used in commercial monitors. However, such systems require calibration, are cumbersome, and are wired to the remote monitor. A single wraparound-type inductive coil or capacitive plate transducer generally cannot provide the required sensitivity due to the fact that the entire coil may move in response to artifact as well as respiratory efforts, which in some cases actually cancels or nullifies the desired respiratory movement detection.
Further, there is generally thought to be an incompatibility between locations on a subject's body for both heart and respiration sensors. The sites that provide good photo sensor heart wave signals (fingers, wrist, ear and foot locations) are believed to be incompatible with sites for acquiring respiration signals (thoracic, umbilicus areas). Therefore prior art attempts to combine these two methods of bio-signal acquisition have required separate sensors at distinctly different areas of the body to be measured.